Interactive haptic feedback systems are known in the prior art for delivering tactile data to a user, such as sensations of force and touch. For example, haptic feedback has been used in the past in various aerospace, surgical and defence applications for the purpose of controlling remote robotic vehicles and manipulators. More recently, haptic feedback has been used in telespresence and virtual reality applications. Telepresence refers to the experience or impression of being present at a real-world location remote from one's own immediate environment. Virtual reality is a similar concept except that its goal is to immerse the user in a simulated, computer-generated world, often for the purposes of entertainment. In all of these applications tactile data is conveyed to a user via human interface devices, such as a gloves or exoskeletans. However, these interface devices are typically bulky or awkward to use or are adapted for very specific applications.
Four different types of mechanoreceptors in the human skin detect tactile stimuli, namely the Meissner corpuscle, the Merkel cell, the Pacinian corpuscle and the Ruffini ending. The Meissner corpuscles and Merkel cells detect light touch and are located beneath the surface of the skin approximately 0.7 mm. Both of these mechanoreceptors transduce very slight inputs of mechanical energy into action potentials. Pacinian corpuscles are located deeper in the skin, typically about 2 mm below the skin surface, and are a type of pressure sensor stimulated by strong pressure. Ruffini endings are a type of mechanoreceptor located around the base of hairs and detect hair movements. Most prior art haptic systems developed thus far do not stimulate human skin mechanoreptors selectively or precisely. Such systems are therefore unsuitable for virtual reality and similar applications where fidelity of tactile sensations is critical.
Some prior art telepresence or telerobotic systems rely on applying vibrotactile stimulation to the user. U.S. Pat. No. 5,619,180, Massimino et al., dated Apr. 8, 1997 describes a system for generating a feedback signal corresponding to a force sensed by an effector in a remote environment. The feedback signal is delivered to the local site of the operator where it is transduced into a vibrotactile sensory substitution signal to which the operator is sensitive. Vibrotactile display elements can be located on the operator's limbs, such as the hands, fingers, arms or legs. The operator therefore “feels” the forces that the effector senses to some degree depending upon the fidelity of the force sensing and reproduction system. Previous artificial tactile displays of this sort have been limited primarily to homogenous arrays of relatively small vibrators that provide low-amplitude, high frequency stimulation of the tactile system. Such vibrotactile systems are useful for some applications, but they do not enable a highly sensitive localized response.
U.S. Pat. No. 4,655,673, Hawkes, dated Apr. 7, 1987, describes a telerobotic apparatus comprising a vibration sensitive transducer. The output signal from the transducer is converted to audible sounds which can be intuitively interpreted by the operator as indicators of texture, hardness and the like. Other tactile display developers have proposed acoustic feedback systems using surface acoustic waves to apply shear stresses to a finger surface of a user.
Prior art devices that rely on applying pneumatic stimulation to the user are also known in the prior art. Some prior art systems direct compressed air to a skin surface in the form of air jets, air cuffs or air bellows. For example, Robert Stone conceived a pneumatic bellows glove in 1989, referred to as Teletact, that employed a plurality of air pockets to provide tactile feedback to the fingers and palm of a user.
Electrotactile or electrocutaneous systems are also known for delivering electrical current to electrodes placed on the user's skin to induce a tactile response. U.S. Pat. No. 4,926,879, Sevrain et al., dated May 22, 1990 describes an electro-tactile stimulator comprising a flexible substrate on one surface of which is formed an electrically conductive pattern having a number of electrodes which are placed in contact with a skin surface of a user. The primary purpose of such electrotactile devices is to assist hearing or vision impaired persons in interpreting environmental stimuli. The specific object of the Sevrain et al. invention is to achieve this result while avoiding skin irritation caused by electrically induced changes in the pH of skin tissue.
U.S. Pat. No. 4,390,756, Hoffmann et al., dated Jun. 28, 1983, relates to an electrocutaneous stimulation apparatus which may be used as a hearing prosthesis by deaf individuals. According to this invention acoustical signals, in particular speech sounds, are encoded into electrocutaneous stimulation patterns. The tactile stimulations are applied via skin surface electrodes, for example on the user's forearm, and can be interpreted as speech information.
U.S. Pat. No. 5,957,812, Harrigan, dated Sep. 28, 1999, relates to an electrical muscle stimulation (EMS) device configured as a vending machine that allows a user to control the amount of electronic impulses required to stimulate the user's muscles to contract and exercise. Other similar electrocutaneous devices for electrically stimulating injured tissue are well-known in the medical and rehabilitation fields. For example, totally implanted pulse generator (IPG) and radio frequency (RF) electrocutaneous systems having been used as spinal cord stimulators and pain relief devices. Subdermal electrocutaneous stimulation has also been used to provide sensory feedback to users of upper extremity neuroprostheses.
Conventional EMS devices, electric massagers and electrocutaneous devices used for tissue rehabilitation purposes and the like employ comparatively few electrodes each applying a relatively large amount of current (e.g. greater than 15 milliamps). The result is the provision of blunt sensations to the user. Most devices are not designed to selectively stimulate all four types of mechanoreceptors in the human skin described above. Moreover, the current applied is pre-programmed and there is no provision for adjustment of the current parameters based on user interactivity or other variable data input.
Although there is a growing awareness of the advantages of electro-neuromodulation therapy for medical or rehabilitative purposes, thus far electrotactile or electrocutaneous devices have not been effectively applied in the information and entertainment industries, such as part of a virtual reality computer application. The need has therefore arisen for an improved electrotactile system useful for virtual reality simulations and the like which overcomes the various limitations of the prior art. Unlike conventional devices, applicant's invention is capable of inducing very sensitive tactile sensations in a user, has network data transfer capability and relatively low current and power requirements, and is operable bidirectionally as both a tactile sensation input and feedback device. Other features and advantages of the invention are described below.